Acetylcholine receptors present in electric tissues and in skeletal muscle are hydrophobic, multisubunit, glycoproteins. The structure of these complexes in detergent solution and in membrane are being determined by hydrodynamic analysis, neutron scattering, chemical cross-linking, and electron microscopic immunohistochemical techniques. Receptors from different species are being compared to determine homologies in polypeptide composition and in the location and nature of the sites binding acetylcholine and alpha-neurotoxins.